Keflex (cephalexin): What it treats and how to use it safely

Keflex, the brand name for cephalexin, is a common oral antibiotic doctors reach for when skin, throat, ear, or some urinary infections are suspected. It works well against many bacteria, acts quickly for the right infections, and is widely available. But like any antibiotic, using Keflex the right way matters — for your health and to avoid resistance.

When doctors prescribe Keflex

You'll most often see Keflex used for skin infections (like cellulitis or infected cuts), strep throat if penicillin can't be used, some ear infections, and simple urinary tract infections. It’s not a one-size-fits-all antibiotic — it won’t help viral illnesses like the common cold or the flu. Your clinician picks it after considering the likely bacteria and any allergies you have.

Typical adult doses are 250–500 mg every 6–12 hours depending on the infection. For some problems doctors may use higher or lower doses and adjust for kidney function. Always follow the exact prescription — don’t halve doses or stop early even if you feel better.

Side effects, allergies, and safety tips

The most common side effects are mild: stomach upset, nausea, diarrhea, or yeast infections. A serious but rare risk is an allergic reaction. If you develop hives, swelling of the face or throat, or trouble breathing, get emergency care. Also watch for severe or bloody diarrhea — that can signal C. difficile, a bacterial overgrowth that needs urgent treatment.

If you’re allergic to penicillin, tell your doctor. Many people with penicillin allergies can still take cephalosporins like Keflex, but it depends on your reaction history. People with kidney problems may need lower doses. If you take blood thinners (warfarin) or certain other drugs, Keflex can change how those medications act — always list your medicines.

Antibiotic stewardship matters. Don’t pressure a clinician for Keflex if your illness is viral. Using antibiotics when they aren’t needed increases resistance and can make future infections harder to treat.

Buying and storing: Keflex usually requires a prescription. If you use an online pharmacy, confirm it’s licensed and requires a prescription. Store capsules at room temperature away from moisture. Finish the prescribed course or follow your doctor’s instructions if they advise stopping earlier.

Pregnancy and breastfeeding: Cephalexin is commonly used in pregnancy and while breastfeeding when indicated, but always check with your provider first. Dose adjustments are sometimes needed for infants or older adults.

Bottom line: Keflex is a reliable antibiotic for many bacterial infections when used correctly. Ask your clinician why it’s chosen, follow the dose and timing, watch for allergic signs or severe diarrhea, and don’t share antibiotics. If symptoms don’t improve in 48–72 hours or get worse, contact your healthcare provider for reassessment.